Adaptive timer for LLC type 2 reliable transport in a computer network

Abstract

A method for computing an ACK timing interval for an ACK timer in a protocol layer LLC type 2 session first measures a time interval between transmission of a frame by a source computer joined to a to a destination computer by an intermediate link, and receipt of a corresponding acknowledgment frame by the source computer from the destination computer. The two events at the source computer, starting a timer upon commencement of transmission of a frame or sequence of frames and the later reception of an acknowledge message indicating receipt of those frames, permits calculation of a measured time interval. The measured time interval is used to compute the bandwidth of the intermediate link. The required ACK timing interval for the ACK timer is then computed in response to the bandwidth, the number of bytes transmitted after starting the ACK timer, and the return time for an acknowledgment message. The ACK timing interval may be recomputed after every transmission of frames and receipt of a corresponding ACK message. The ACK timing interval is thereby dynamically adjusted to conditions on the intermediate link, including natural bandwidth for either a slow or fast link, congestion due to other traffic on the link, etc. The dynamic adjustment of the ACK timing interval prevents inadvertent timeouts of the ACK timer, and so prevents inadvertent breaking of the LLC type 2 reliable transport connection.

What is claimed is:  
     
       1. A method for computing a timing interval for an ACK timer in a protocol layer LLC type 2 reliable transport session, comprising: 
       measuring a time interval between transmission of a frame by a source computer to a destination computer, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer, said time interval measured by said source computer;  
       computing a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       computing said timing interval in response to said bandwidth.  
     
     
       2. A computer readable media containing a computer executable computer program for the practice of the method of  claim 1 . 
     
     
       3. Electromagnetic signals propagating over a computer network, said electromagnetic signals carrying information for execution in a processor to practice the method of  claim 1 . 
     
     
       4. A method for establishing a timing interval for a retransmission timer in a protocol layer LLC type 2 session, comprising: 
       measuring a time interval (designated as TRT) between transmission of a frame by a source computer to a destination computer, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer;  
       computing a bandwidth (designated as A) of the intermediate link in response to said time interval by the formula,  
       
         
             A  (bytes/sec) 13 =(Number of bytes transmitted in round trip)/TRT;  
         
       
        and,  
       computing said timing interval (designated TOUT) for said retransmission timer by the formula:  
       
         
             T OUT(Number of bytes per packet)/ A )+(time adder for uncertainty),  
         
       
        where “Number of bytes per packet” is the number of bytes to be subsequently transmitted with acknowledgment.  
     
     
       5. The method as in  claim 4  further comprising: 
       computing said “time adder for uncertainty” as a selected percentage of the term,  
       
         
           (Number of bytes per packet)/ A ).  
         
       
     
     
       6. The method as in  claim 5  further comprising: selecting said percentage in response to a percentage of timeouts occurring at said source computer. 
     
     
       7. The method of  claim 4  further comprising: 
       selecting said “time adder for uncertainty” as zero.  
     
     
       8. An apparatus to adapt an acknowledgment message timing interval to a measurement of packet round trip time in a protocol layer LLC type 2 reliable transport session, comprising: 
       means for measuring a time interval between transmission of a frame by a source computer to a destination computer, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer, said time interval measured by said source computer;  
       means for computing a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       means for computing said timing interval in response to said bandwidth.  
     
     
       9. An apparatus to adapt an acknowledgment message timing interval to a measurement of packet round trip time in a protocol layer LLC type 2 reliable transport session, comprising: 
       a time interval determining device in a source computer to measure a time interval between transmission of a frame by said source computer to a destination computer, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer;  
       a first computation unit in said source computer to compute a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       a second computation unit in said source computer to compute said timing interval in response to said bandwidth.  
     
     
       10. A computer readable media containing a computer program to perform a calculation of a timing interval for a method of adapting a timing interval of an ACK timer in a protocol layer LLC type 2 reliable transport session, comprising: 
       measuring a time interval between transmission of a frame by a source computer to a destination computer, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer, said time interval measured by said source computer;  
       computing a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       computing said timing interval in response to said bandwidth.  
     
     
       11. Electronic signals on a computer network, said electronic signals transmitted to a computer, said signals transmitting a computer program to perform a calculation of a timing interval for a method of adapting a timing interval of an ACK timer in a protocol layer LLC type 2 reliable transport session, comprising: 
       measuring a time interval between transmission of a frame by a source computer to a destination computer, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer, said time interval measured by said source computer;  
       computing a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       computing said timing interval in response to said bandwidth.  
     
     
       12. A method for computing a timing interval for an ACK timer in a protocol layer LLC type 2 reliable transport session, comprising: 
       measuring a time interval between transmission of a frame by a source computer using a LLC type 2 reliable transport session to a destination computer also using a LLC type 2 reliable transport session, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer, said time interval measured by said source computer;  
       computing a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       computing said timing interval in response to said bandwidth.  
     
     
       13. A method for establishing a timing interval for a retransmission timer in a protocol layer LLC type 2 session, comprising: 
       measuring a time interval (designated as TRT) between transmission of a frame by a source computer using a LLC type 2 reliable transport session to a destination computer also using a LLC type 2 reliable transport session, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer;  
       computing a bandwidth (designated as A) of the intermediate link in response to said time interval by the formula,  
       
         
             A (bytes/sec)_=(Number of bytes transmitted in round trip)/TRT;  
         
       
        and,  
       computing said timing interval (designated TOUT) for said retransmission timer by the formula:  
       
         
             T OUT=(Number of bytes per packet)/ A )+(time adder for uncertainty),  
         
       
        where “Number of bytes per packet” is the number of bytes to be subsequently transmitted with acknowledgment.  
     
     
       14. An apparatus to adapt an acknowledgment message timing interval to a measurement of packet round trip time in a protocol layer LLC type 2 reliable transport session, comprising: 
       means for measuring a time interval between transmission of a frame by a source computer using a LLC type 2 reliable transport session to a destination computer also using a LLC type 2 reliable transport session, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer, said time interval measured by said source computer;  
       means for computing a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       means for computing said timing interval in response to said bandwidth.  
     
     
       15. An apparatus to adapt an acknowledgment message timing interval to a measurement of packet round trip time in a protocol layer LLC type 2 reliable transport session, comprising: 
       a time interval determining device in a source computer to measure a time interval between transmission of a frame by said source computer using a LLC type 2 reliable transport session to a destination computer also using a LLC type 2 reliable transport session, and receipt of a corresponding acknowledgment frame by said source computer from said destination computer;  
       a first computation unit in said source computer to compute a dynamic bandwidth of a connection between said source computer and said destination computer in response to said time interval; and,  
       a second computation unit in said source computer to compute said timing interval in response to said bandwidth.